Auxiliary torch ignition

ABSTRACT

A torch igniter includes an auxiliary fuel injector; an ignition source; and an igniter body carrying the auxiliary fuel injector and the ignition source. The igniter body includes an auxiliary combustion chamber having a side wall extending axially from a first end wall to a second end wall. In some examples, at least a portion of the side wall includes a distributed pattern of cooling apertures, with each of the cooling apertures extending obliquely from an outer surface of the side wall to an inner surface of the side wall. In some examples, the second end wall defines a fluid outlet leading to an outlet tube in fluid communication with the primary combustion chamber, at least a portion of the outlet tube including a distributed pattern of dilution apertures.

TECHNICAL FIELD

This specification generally relates to combustor assemblies for gasturbine engines that incorporate auxiliary torch ignition systems tofacilitate ignition in a main combustion chamber.

BACKGROUND

The gas turbine engine is the preferred class of internal combustionengine for many high power applications. Fundamentally, the gas turbineengine features an upstream rotating compressor coupled to, andtypically driven by, a downstream turbine, with a combustion chamberresiding in-between the two rotary components. A torch igniter is adevice that may be used to ignite the primary combustor of a gas turbineengine. In some applications, the torch igniter has advantages overconventional spark igniters, because it can provide larger amounts ofenergy release to the main combustor, and thus, is capable of lightingthe engine in a more reliable manner. To achieve this, the torch igniterrequires an auxiliary source of fuel and air, as well as an ignitionsource. Auxiliary air flow is typically obtained from the plenumdownstream of the engine's compressor or from an external source ofcompressed air; and the auxiliary fuel is obtained from thefuel-metering unit or manifold or from an independent fuel source. Airflow requirements to operate the torch igniter may vary under differentconditions, but are often significantly less than the air flowrequirements of the primary combustor. On a typical engine, much like aconventional spark igniter, there can be two or more torch igniters forredundancy.

SUMMARY

In one aspect, a gas turbine combustor assembly includes: a primarycombustion chamber in fluid communication with a primary fuel injectorand a primary air inlet; and a torch ignitor coupled to the primarycombustion chamber. The torch igniter includes: an auxiliary fuelinjector; an ignition source; and an igniter body carrying the auxiliaryfuel injector and the ignition source. The igniter body includes anauxiliary combustion chamber having a side wall extending axially from afirst end wall to a second end wall, at least a portion of the side wallincluding a distributed pattern of cooling apertures, with each of thecooling apertures extending obliquely from an outer surface of the sidewall to an inner surface of the side wall, so as to cause fluid enteringan interior cavity of the auxiliary combustion chamber through thecooling apertures to form a fluid film along the inner surface.

In some examples, the combustor assembly further includes a premixingcup residing within the interior cavity of the auxiliary combustionchamber. In some examples, the premixing cup includes a cylindrical wallradially surrounding the auxiliary fuel injector and an auxiliary airinlet, the cylindrical wall of the premixing cup protruding axiallyoutward relative to the first end wall of the auxiliary combustionchamber through a portion of the interior cavity to delineate apremixing zone radially inward of the cylindrical wall and arecirculation zone radially outward of the cylindrical wall, with theignition source residing on the side wall of the auxiliary combustionchamber at a position proximate the recirculation zone

In some examples, the auxiliary combustion chamber is substantiallycylindrical in shape, with the side wall having a circular cross-sectionof constant diameter, and the first and second end walls beingsubstantially planar.

In some examples, the second end wall defines a fluid outlet leading toan outlet tube in fluid communication with the primary combustionchamber. In some examples, the igniter body further includes an outershell surrounding at least a portion of the auxiliary combustionchamber, the outer shell including a fluid inlet coaxially aligned withthe outlet tube. In some examples, the igniter body includes a fluidannulus formed between an inner surface of the shell and an outersurface of the auxiliary combustion chamber, the annulus directing fluidfrom the fluid inlet across the outer surface of the auxiliarycombustion chamber towards the first end wall.

In some examples, the second end wall of the auxiliary combustionchamber defines a fluid outlet leading to an outlet tube in fluidcommunication with the primary combustion chamber, at least a portion ofthe outlet tube including a distributed pattern of dilution apertures,with each of the dilution apertures configured to direct fluid incross-flow with heated gas exiting the auxiliary combustion chamberthrough the outlet tube.

In some examples, the igniter body further includes a fluid swirlerresiding at an entrance to a premixing cup residing within the auxiliarycombustion chamber. In some examples, the fluid swirler includes anaxial fluid swirler including a circumferential pattern of swirl openingsurrounding an outlet of the auxiliary fuel injector.

In some examples, the torch igniter further includes a shielding deviceconfigured to at least partially shield the ignition source from fluidflow through the auxiliary combustion chamber. In some examples, theshielding device is coupled to an inner surface of the auxiliarycombustion chamber proximate the ignition source, and includes a curved,convex surface.

In another aspect, a gas turbine combustor assembly includes: a primarycombustion chamber in fluid communication with a primary fuel injectorand a primary air inlet; and a torch ignitor coupled to the primarycombustion chamber. The torch igniter includes: an auxiliary fuelinjector; an ignition source; and an igniter body carrying the auxiliaryfuel injector and the ignition source. The igniter body includes anauxiliary combustion chamber having a side wall extending axially from afirst end wall to a second end wall, the second end wall defining afluid outlet leading to an outlet tube in fluid communication with theprimary combustion chamber, at least a portion of the outlet tubeincluding a distributed pattern of dilution apertures, with each of thedilution apertures configured to direct fluid in cross-flow with heatedgas exiting the auxiliary combustion chamber through the outlet tube.

In some examples, the combustor assembly further includes a premixingcup residing within an interior cavity of the auxiliary combustionchamber. In some examples, the premixing cup includes a cylindrical wallradially surrounding the auxiliary fuel injector and an auxiliary airinlet, the cylindrical wall of the premixing cup protruding axiallyoutward relative to the first end wall of the auxiliary combustionchamber through a portion of the interior cavity to delineate apremixing zone radially inward of the cylindrical wall and arecirculation zone radially outward of the cylindrical wall, with theignition source residing on the side wall of the auxiliary combustionchamber at a position proximate the recirculation zone.

In some examples, the auxiliary combustion chamber is substantiallycylindrical in shape, with the side wall having a circular cross-sectionof constant diameter, and the first and second end walls beingsubstantially planar.

In some examples, the second end wall defines a fluid outlet leading toan outlet tube in fluid communication with the primary combustionchamber. In some examples, the igniter body further includes an outershell surrounding at least a portion of the auxiliary combustionchamber, the outer shell including a fluid inlet coaxially aligned withthe outlet tube. In some examples, the igniter body includes a fluidannulus formed between an inner surface of the shell and an outersurface of the auxiliary combustion chamber, the annulus directing fluidfrom the fluid inlet across the outer surface of the auxiliarycombustion chamber towards the first end wall.

In some examples, at least a portion of the side wall of the auxiliarycombustion chamber includes a distributed pattern of cooling apertures,with each of the cooling apertures obliquely canted relative to an innersurface of the side wall so as to cause fluid entering an interiorcavity of the auxiliary combustion chamber through the cooling aperturesto form a fluid film along the inner surface.

In some examples, the igniter body further includes a fluid swirlerresiding at to an entrance to a premixing cup residing within theauxiliary combustion chamber. In some examples, the fluid swirlerincludes an axial fluid swirler including a circumferential pattern ofswirl opening surrounding an outlet of the auxiliary fuel injector.

In some examples, the torch igniter further includes a shielding deviceconfigured to at least partially shield the ignition source from fluidflow through the auxiliary combustion chamber. In some examples, theshielding device is coupled to an inner surface of the auxiliarycombustion chamber proximate the ignition source, and includes a curved,convex surface.

In yet another aspect, a method of operating a gas turbine combustorassembly includes the steps of: mixing auxiliary fuel and air flows inan auxiliary combustion chamber to form an auxiliary fuel/air mixture;igniting the auxiliary fuel/air mixture to form an auxiliary flow ofheated fluid; directing the auxiliary flow of heated fluid through theauxiliary combustion chamber towards a primary combustion chamber; whiledirecting the auxiliary flow of heated fluid, receiving a flow ofcooling fluid, and directing the cooling fluid so as to form a film ofcooling fluid along an inner surface of the auxiliary combustion chamberand dilute the auxiliary flow of heated fluid; and igniting a primaryair/fuel mixture in a primary combustion chamber of the gas turbinecombustor assembly with the diluted auxiliary flow of heated fluid fromthe auxiliary combustion chamber.

In still yet another aspect, a gas turbine combustor assembly includes:a primary combustion chamber in fluid communication with a primary fuelinjector and a primary air inlet; and a torch ignitor coupled to theprimary combustion chamber. The torch igniter includes: an auxiliaryfuel injector; an ignition source; and an igniter body carrying theauxiliary fuel injector and the ignition source. The igniter bodyincludes an auxiliary combustion chamber having a side wall extendingaxially from a first end wall to a second end wall, the side walldefining an interior cavity between the first and second end walls. Theigniter body further includes a premixing cup residing within theinterior cavity including a cylindrical wall radially surrounding theauxiliary fuel injector and an auxiliary air inlet, the cylindrical wallof the premixing cup protruding axially outward relative to the firstend wall of the auxiliary combustion chamber through a portion of theinterior cavity to delineate a premixing zone radially inward of thecylindrical wall and a recirculation zone radially outward of thecylindrical wall, with the ignition source residing on the side wall ofthe auxiliary combustion chamber at a position proximate therecirculation zone.

In some examples, the torch igniter further includes an auxiliary fuelsource in fluid communication with a nozzle orifice of the auxiliaryfuel injector, the auxiliary fuel source configured to provide apressurized flow of fuel for injection into the auxiliary combustionchamber by the auxiliary fuel injector; and a bypass line configured toreturn at least a portion of the pressurized flow of fuel to a mainengine fuel manifold.

In some examples, the auxiliary combustion chamber is substantiallycylindrical in shape, with the side wall having a circular cross-sectionof constant diameter, and the first and second end walls beingsubstantially planar.

In some examples, the second end wall defines a fluid outlet leading toan outlet tube in fluid communication with the primary combustionchamber. In some examples, the igniter body further includes an outershell surrounding at least a portion of the auxiliary combustionchamber, the outer shell including a fluid inlet coaxially aligned withthe outlet tube. In some examples, the igniter body includes a fluidannulus formed between an inner surface of the shell and an outersurface of the auxiliary combustion chamber, the annulus directing fluidfrom the fluid inlet across the outer surface of the auxiliarycombustion chamber towards the first end wall.

In some examples, the second end wall of the auxiliary combustionchamber defines a fluid outlet leading to an outlet tube in fluidcommunication with the primary combustion chamber. In some examples, atleast a portion of the outlet tube includes a distributed pattern ofdilution apertures, with each of the dilution apertures configured todirect fluid in cross-flow with heated gas exiting the auxiliarycombustion chamber through the outlet tube.

In some examples, the igniter body further includes a fluid swirlerresiding at an entrance to the premixing cup. In some examples, thefluid swirler includes an axial fluid swirler including acircumferential pattern of swirl opening surrounding an outlet of theauxiliary fuel injector.

In some examples, the torch igniter further includes a shielding deviceconfigured to at least partially shield the ignition source from fluidflow through the auxiliary combustion chamber. In some examples, theshielding device is coupled to an inner surface of the auxiliarycombustion chamber proximate the ignition source, and includes a curved,convex surface projecting towards the premixing cup.

In some examples, at least a portion of the side wall of the auxiliarycombustion chamber includes a distributed pattern of cooling apertures,with each of the cooling apertures obliquely canted relative to an innersurface of the side wall so as to cause fluid entering an interiorcavity of the auxiliary combustion chamber through the cooling aperturesto form a fluid film along the inner surface.

In yet another aspect still, a method of operating a gas turbinecombustor assembly includes the steps of: receiving auxiliary flows offuel and air in a premixing cup of an igniter body of the gas turbinecombustor assembly; at least partially mixing the auxiliary fuel and airflows in a premixing zone of the premixing cup, and discharging theauxiliary fuel/air mixture into an auxiliary combustion chamber of theigniter body; directing the discharged auxiliary fuel/air mixture into aprimary recirculation zone including an annular space between thepremixing cup and an inner surface of the auxiliary combustion chamber;igniting the auxiliary fuel/air mixture at a location proximate theprimary recirculation zone to form an auxiliary flow of heated fluid;and igniting a primary air/fuel mixture in a primary combustion chamberof the gas turbine combustor assembly with the auxiliary flow of heatedfluid from the auxiliary combustion chamber of the igniter body.

In some examples, receiving the auxiliary flow of fuel includes thesteps of: directing a pressurized flow of fuel from an auxiliary fuelsource to a nozzle orifice of an auxiliary fuel injector in fluidcommunication with the premixing cup, bypassing the nozzle orifice withat least a portion of the fuel flow, and directing the bypassed portionof the fuel flow to a main engine fuel manifold.

In some examples, receiving the auxiliary flow of air includes directingthe air through a fluid inlet. In some examples, the method furtherincludes directing the auxiliary flow of heated fluid through a fluidoutlet tube coaxially aligned with the fluid inlet as the auxiliary flowof air is directed through the fluid inlet.

In some examples, the method further includes diluting the auxiliaryflow of heated fluid by directing a portion of the auxiliary flow of airin cross-flow with the auxiliary flow of heated flow through a patternof dilution apertures of the outlet tube.

In some examples, the method further includes cooling a portion of theauxiliary combustion chamber by forming a cooling fluid film along aninner surface of the auxiliary combustion chamber. In some examples,forming the cooling fluid film includes directing a portion of theauxiliary flow of air through a distributed pattern of obliquely cantedcooling apertures of the auxiliary combustion chamber

In some examples, at least partially mixing the auxiliary fuel and airflows includes inducing a swirling flow pattern in each of the flows

In some examples, igniting the auxiliary fuel/air mixture includesenergizing an ignition source while at least partially shielding theignition source from the auxiliary fuel/air mixture.

The details of one or more implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the description below. Other features, aspects, andadvantages of the subject matter will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a half, side cross-sectional view of an example gas turbineengine.

FIG. 2A is a half, side cross-sectional view of a first example torchigniter.

FIG. 2B is an enlarged view of the portion of FIG. 2A marked 2B-2B.

FIG. 3 is a diagram illustrating a velocity flow field achieved byoperation of a second example torch igniter.

FIG. 4 is a half, side cross-sectional view of a third example torchigniter system.

DETAILED DESCRIPTION

In a gas turbine engine, the torch igniter ignites fuel released bycombustor nozzles in a combustor of the engine to produce heatedcombustion products. The heated combustion products are, in turn,expanded through a turbine of the engine to produce torque. Reliableignition and flame propagation around the primary combustor nozzles inconditions with relatively low air pressure drop (delta P) may require aheightened minimum level of ignition energy provided to the operatingenvelope. This concern is often exacerbated when the ambient environmentis particularly cold. In order to provide sufficient ignition energyacross a broad range of operating conditions in different ambientenvironments, high-quality flame stability/operability of the torchigniter system is desired.

In certain aspects, the present disclosure relates to torch ignitersystems that supply high ignition energy by incorporating variouscombinations of design features in the igniter body. In someimplementations, for example, the igniter body includes an auxiliarycombustion chamber with a premixing cup that directs a mixture of fueland air into a recirculation zone proximate an ignition source. Theentrance to the premixing cup may include an air swirler to enhancerecirculation and mixing of the auxiliary air and fuel flows in theauxiliary combustion chamber.

In some implementations, optimization of the turbulence and swirlingcomponents is achieved to sustain the torch igniter flame without havingto keep the ignition source on. In some implementations, a torch igniterin accordance with one or more embodiments of the present disclosure canimprove cold day combustor light off performance, and provide reliablere-light capability across a wide range of operating conditions byproviding high energy release that is enhanced by swirl stabilizedcombustion in the torch combustor.

Further, certain torch igniter systems of the present disclosureincorporate design features that extend the operational life ofcomponents having high-temperature failure mechanisms. For instance, insome implementations, a side wall of the auxiliary combustion chamberincludes a pattern of distributed cooling apertures. As discussed indetail below, the cooling apertures can be configured to enable coolingfluid (e.g., air) to contact the inner surface of the auxiliarycombustion chamber without adversely affecting the combustion conditionstherein (e.g., fuel/air ratio, air/fuel temperatures, air/fuel flowvelocities, etc.). As another example, in some implementations, anoutlet tube receiving the combustion products from the auxiliarycombustion chamber includes a pattern of dilution apertures. Thedilution apertures on the outlet tube can be configured to facilitatemixing of a dilution fluid (e.g., air) with the combustion products toeffect a temperature change.

FIG. 1 is a half, side cross-sectional view of an example gas turbineengine 10. The gas turbine engine 10 is turbojet-type gas turbine thatcould be used, for example, to power jet aircrafts. However, it isappreciated that the concepts described in the present disclosure arenot so limited, and can be incorporated in the design of various othertypes of gas turbine engines (e.g., turbofan, turboprop, turboshaft, orindustrial/marine engines).

As shown, the gas turbine engine 10 generally facilitates a continuousaxial flow of gas. That is, gas generally flows through the engine 10 inthe axially downstream direction indicated by the arrows in FIG. 1. Thegas turbine engine 10 includes an intake 12 that receives ambient air 14and directs the ambient air to a compressor 16. The ambient air 14 isdrawn through multiple stages of the compressor 16. High-pressure air 18exiting the compressor 16 is introduced to a combustor 100. In certaininstances, the combustor 100 is an annular combustor circumscribing theengine's main shaft 20 or a can-type combustor positioned radiallyoutward of the shaft.

The combustor 100 includes a combustion shield 102, multiple fuelinjectors 104, a combustor dome 106, and a torch igniter system 108. Atthe combustor 100, the high-pressure air 18 is mixed with liquid orgaseous fuel (not shown) and ignited by the torch igniter system 108 toproduce heated combustion products 22. The combustion products 22 arepassed through multiple stages of a turbine 24. The turbine 24 extractsenergy from the high-pressure, high-temperature combustion products 22.Energy extracted from the combustion products 22 by the turbine 24drives the compressor 16, which is coupled to the turbine by the mainshaft 20. Exhaust gas 26 leaving the turbine 24 is accelerated into theatmosphere through an exhaust nozzle 28 to provide thrust or propulsionpower or energy for electrical power generation.

FIGS. 2A-2B show an example torch igniter 200 that can be used in thetorch igniter system 108 of FIG. 1. In certain instances, the torchigniter system 108 includes multiple, spaced apart torch igniters 200.In this example, the torch igniter 200 includes an igniter body 202, anauxiliary fuel injector 204, and an ignition source 206. The igniterbody 202 includes a main housing 208 outlining a hollow, substantiallycylindrical interior cavity but could be different shape based onphysical envelope requirement. The interior cavity of the main housing208 receives an auxiliary combustion chamber 210. An annular gap betweenthe outer surface of the auxiliary combustion chamber 210 and the innersurface of the housing 208 defines a fluid passage 212. The fuelinjector 204 and ignition source 206 are supported by the housing 208.The ignition source 206, for example, is mounted directly to the housing208, extending through an opening in the housing's side wall. Atemperature sensor 213 (e.g., a thermocouple) is similarly mounted tothe housing 208. The auxiliary fuel injector 204 is coupled to thehousing 208 via a mounting bracket 214. That is, the mounting bracket214 carries the fuel injector 204 and is directly attached (bolted, inthis example) to the front end of the main housing 208.

In this example, the auxiliary fuel injector 204 includes a nozzleorifice 216, a fuel inlet line 218 and a fuel bypass line 220. The fuelinlet 218 is placed in fluid communication with a pressurized source offuel (not shown). During use, pressurized fuel from the source flowstoward the nozzle orifice 216 via the fuel inlet line 218. At least aportion of this fuel flow bypasses the nozzle orifice 216 and isreturned to the main engine fuel manifold by the fuel bypass line 220.In some examples, the fuel injector incorporates additional designfeatures for enhancing fuel atomization and increasing fuel turn downratio to meet fuel flow requirement at all operating conditions withoutchanging the size of the nozzle orifice 216, which may otherwise inducecoking.

The auxiliary combustion chamber 210 received within the interior of themain housing 208 features a cylindrical body including a curved sidewall 226 extending between substantially planar front and rear end walls228,230. The cylindrical body of the auxiliary combustion chamber 210defines an axial length “L” and a radial diameter “D”. In some examples,the volume and/or the L/D ratio of the auxiliary combustion chamber 210may affect flame stabilization. For example, flame stabilization can beimproved by providing the auxiliary combustion chamber 210 with a volumeand/or an L/D ratio that reduces the reference velocity of the fluid(i.e., the theoretical flow velocity of air through an area equal to themaximum cross section of the combustor casing). Improved flamestabilization may enable the torch igniter 200 to sustain the flame athigher pressure drop conditions, which increases the operating envelopeof the primary combustor.

The igniter body 202 further includes an end cap provided in the form ofa bulkhead 232 bolted to the rear end of the main housing 208. Thebulkhead 232 generally closes off the interior cavity of the housing 208with the exception of a central through-bore 234. As shown, the bore 234of the bulkhead 232 receives an outlet tube 236 extending from a fluidoutlet 237 at the rear end wall 230 of the auxiliary combustion chamber210. The outlet tube 236 conveys heated fluid from the auxiliarycombustion chamber 210 to the primary combustor. Notably, the innerdiameter of the bulkhead's bore 234 is slightly larger than the outerdiameter of the outlet tube 236, such that a narrow annular gapproviding a fluid inlet 238 is formed therebetween (see FIG. 2B). Thefluid inlet 238 is in fluid communication with the annular fluid passage212 between the housing 208 and auxiliary combustion chamber 210. Thisconfiguration places the fluid inlet 238 and fluid outlet 237 of theigniter body 202 in a coaxial arrangement. Thus, a single opening in theouter shell (the main housing 208 and bulkhead 232) of the igniter body202 is used to route fluid both to and from the auxiliary combustionchamber 210. The design of the bulkhead 232 is modular and applicationspecific. This coaxial design effectively simplifies the manufacturingand assembly process, provides a compact form factor, and alsofacilitates crossflow between the two fluid flows. As explained indetail below in connection with FIG. 4, the cross flowing fluid enablesincoming auxiliary air flow to be used for cooling and/or dilutionpurposes.

A premixing cup 240 resides within the interior of the auxiliarycombustion chamber 210 proximate the chamber's planar front end wall228. The premixing cup 240 includes an air inlet 242 and a cylindricalwall 244. The air inlet 242 radially surrounds the auxiliary fuelinjector 204. The cylindrical wall 244 circumscribes the air inlet 242,and therefore also surrounds the fuel injector 204 radially. An airswirler 246 is positioned within the air inlet 242. In this example, theair swirler 246 has a disk-shaped body including a plurality of swirlopenings arranged in a circumferential pattern. The swirl openingsradially surround the outlet of the auxiliary fuel injector 204 and areoriented generally axially, at a canted, non-zero angle relative to thelongitudinal axis of the auxiliary combustion chamber 210. Thus, theswirl openings are arranged to form a flow vortex along the longitudinalaxis of the auxiliary combustion chamber 210. U.S. Patent PublicationNo. 2016/0047318, the entirety of which is incorporated herein byreference, describes an axial air swirler suitable for use inconjunction with embodiments of the present disclosure.

The cylindrical wall 244 of the premixing cup 240 protrudes axiallyoutward relative to the front end wall 228 of the auxiliary combustionchamber 210 to extend through a frontal portion of the auxiliarycombustion chamber's interior cavity. The cylindrical wall 244delineates two discrete zones within the frontal portion in theauxiliary combustion chamber 210—a premixing zone 248 that is radiallyinward of the cylindrical wall and a recirculation zone 250 that isradially outward of the cylindrical wall. The premixing zone 248provides a compact area for introducing the auxiliary flow of air toatomized fuel from the fuel injector 204, which enhances the degree offuel/air mixing. When the mixed flow of air and fuel is expelled fromthe premixing cup 440 it immediately enters a downstream portion of theauxiliary combustion chamber 210. The empty space in the recirculationzone 250 draws a portion of the fuel/air mixture backwards in theauxiliary combustion chamber towards the chamber's front wall 228,creating a turbulent, toroidal flow pattern (see FIG. 3). Thisrecirculating flow sustains combustion without having to maintain theignition source 206 in an “on” condition, because a portion of theignited air/fuel flow is recirculated back into the incoming fuel flowfrom the premixing zone 248. Even further, the turbulence andrecirculation tends to mix the combusting air/fuel with uncombustedair/fuel, which more evenly ignites the air/fuel mixture throughout theauxiliary combustion chamber 210. This produces stronger, higher energycombustion.

The diagram of FIG. 3 illustrates how fluid flows through a torchignitor 300, which is similar in construction to the torch igniter 200of FIGS. 2A and 2B. As shown in FIG. 3, an auxiliary flow of air entersan igniter body 302 of the torch igniter 300 via a fluid inlet 338. Theauxiliary air flows from the fluid inlet 338 into an annular fluidpassage 312. The fluid passage 312 directs the auxiliary airflow towardsthe air inlet of a premixing cup 340 where it is introduced to an axialair swirler 346. The auxiliary air traverses the air swirler 346 andflows into a mixing zone 348 defined by a cylindrical wall 344 of thepremixing cup 340. In the mixing zone 348, the swirling auxiliaryairflow meets and mixes with atomized fuel discharged from the auxiliaryfuel injector 314. The fuel/air mixture flows from the mixing zone 348into the remaining area of the auxiliary combustion chamber's interiorcavity, including a recirculation zone 350 radially separated from thepremixing zone 348 by the cylindrical wall 344. The fuel/air mixture isenergized (e.g., ignited) by the ignition source, which is positioned inthe auxiliary combustion chamber 310 proximate the recirculation zone350. Heated fluid then flows through the auxiliary combustion chamber310 towards the fluid outlet 337 and into the outlet tube 336, whichleads to the primary combustion chamber.

FIG. 4 shows another example torch igniter 400. Like the previousexamples, torch igniter 400 includes an igniter body 402, an auxiliaryfuel injector 404, and an ignition source 406. The igniter body 402includes a main housing 408 and a bulkhead 432 enclosing a hollowinterior cavity containing an auxiliary combustion chamber 410. Thebulkhead 432 includes a central bore 434 that receives an outlet tube436 leading from the auxiliary combustion chamber 410. The respectiveannular gaps between the auxiliary combustion chamber 420 and thebulkhead 432 and main housing 408 define a fluid inlet 438 leading to afluid passage 412. The interior of the auxiliary combustion chamber 410includes a premixing cup 440 having an air inlet 442 receiving an airswirler 446. The premixing cup 440 further includes an axiallyprotruding cylindrical wall 444 delineating a frontal portion of theauxiliary combustion chamber into a mixing zone 448 and a recirculationzone 450.

In this example, the auxiliary fuel injector 404 incorporates additionaldesign features and control scheme for enhancing fuel atomization andincreasing fuel turn down ratio to meet fuel flow requirement at alloperating conditions without changing the size of the nozzle orifice,which may otherwise induce coking.

In this example, the curved side wall 426 of the auxiliary combustionchamber 410 includes a distributed pattern of cooling apertures 452. Thecooling apertures 452 project through the side wall 426 of the auxiliarycombustion chamber 410, enabling a portion of the auxiliary air flowtraversing the annular fluid passage 412 to enter the auxiliarycombustion chamber 410. In this example, each of the cooling apertures452 is obliquely canted relative to the inner surface of the chamber'scurved side wall 426. The angled orientation of the cooling apertures452 causes air entering the auxiliary combustion chamber 410therethrough to form a fluid film along the chamber's inner surface. Thefilm of auxiliary air adheres to the inner surface of the auxiliarycombustion chamber 410, and therefore is inhibited from comingling withthe air/fuel mixture flowing from the premixing cup 440. This allows theauxiliary airflow to cool the auxiliary combustion chamber 410 withoutaffecting the stoichiometry of the combustion process. The distributionof cooling apertures may vary between different implementations. Forexample, different implementations may employ more or less coolingapertures without departing from the scope of the present disclosure.Moreover, in some implementations, the distribution of cooling aperturesmay vary across the length of the auxiliary combustion chamber. Forinstance, in this example, the density of cooling apertures increasesfrom the front end of the auxiliary combustion chamber 410 towards therear end.

In addition to the cooling apertures 452, torch igniter 400 furtherincludes a plurality of dilution apertures 454. In this example, thedilution apertures 454 are located along the outlet tube 436 thatconveys heated fluid from the auxiliary combustion chamber 410 to theprimary combustor. The dilution apertures 454 are configured to divert aportion of the auxiliary air flow from the annular fluid inlet 438.Unlike the cooling apertures 452, the dilution apertures 454 aredesigned to direct the incoming air into the flowpath of heated fluidexiting the auxiliary combustion chamber through the outlet tube 436.For example, the dilution apertures 454 may be substantiallyperpendicular to the curved surface of the outlet tube 436, as opposedto obliquely canted. The auxiliary air flow mixes with the heated fluidand dilutes the composition, which results in a relatively swift drop intemperature.

While the embodiment of FIG. 4 provides cooling apertures along theauxiliary combustion chamber and dilution apertures along the outlettube, various other configurations are also contemplated within thescope of the present disclosure. Indeed, either or both of the auxiliarycombustion chamber and outlet tube may include cooling and/or dilutionapertures in different implementations.

The torch igniter 400 still further includes a shielding device 456residing within the interior cavity of the auxiliary combustion chamber410. The shielding device 456 is designed to at least partially shieldthe ignition source 406 from direct contact with the air/fuel mixtureflowing from the premixing cup 440. In this example, the shieldingdevice 456 includes curved body having a convex outer surface facing thepremixing cup 440. As shown, the shielding device 456 further includesmultiple apertures 458 distributed along the body that permit a limitedportion of the fuel/air mixture to flow passed the tip of the ignitionsource 406. In some implementations, shielding the ignition source 406in this way inhibits quenching that tends to occur at relatively coldfuel and air conditions and/or high pressure drop conditions.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the inventions.

What is claimed is:
 1. A gas turbine combustor assembly, comprising: aprimary combustion chamber in fluid communication with a primary fuelinjector and a primary air inlet; and a torch igniter coupled to theprimary combustion chamber, the torch igniter comprising: an auxiliaryfuel injector; an ignition source; and an igniter body carrying theauxiliary fuel injector and the ignition source, the igniter bodycomprising: an auxiliary combustion chamber having a side wall extendingaxially from a first end wall to a second end wall defining a fluidoutlet leading to an outlet tube in fluid communication with the primarycombustion chamber wherein a premixing cup resides in the auxiliarycombustion chamber, an outer shell comprising a fluid inlet coaxiallyaligned with the outlet tube, and a fluid annulus defined by an innersurface of the shell and an outer surface of the auxiliary combustionchamber, the annulus directing an upstream fluid flow from the fluidinlet towards the first end wall, wherein at least a portion of theoutlet tube comprises a distributed pattern of dilution aperturesconfigured to route a first portion of the upstream fluid flow from thefluid annulus into a downstream flow of heated gas exiting the auxiliarycombustion chamber through the outlet tube, and wherein at least aportion of the side wall comprises a distributed pattern of coolingapertures, with each of the cooling apertures extending obliquelythrough the side wall of the auxiliary combustion chamber, so as tocause a second portion of the upstream fluid flow entering an interiorcavity of the auxiliary combustion chamber from the fluid annulusthrough the coding apertures to form a fluid film along an inner surfaceof the side wall.
 2. The combustor assembly of claim 1, furthercomprising: a premixing cup residing within the interior cavity of theauxiliary combustion chamber, the premixing cup comprising a cylindricalwall radially surrounding the auxiliary fuel injector and an auxiliaryair inlet, the cylindrical wall of the premixing cup protruding axiallyoutward relative to the first end wall of the auxiliary combustionchamber through a portion of the interior cavity to delineate apremixing zone radially inward of the cylindrical wall and arecirculation zone radially outward of the cylindrical wall, with theignition source residing on the side wall of the auxiliary combustionchamber at a position proximate the recirculation zone.
 3. The combustorassembly of claim 2, wherein the recirculation zone is a space definedby the first end wall of the auxiliary combustion chamber, the side wallof the auxiliary combustion chamber, and the cylindrical wall of thepremixing cup, the space of the recirculation zone configured to drawfuel/air mixture expelled downstream from the premixing cup backupstream toward the first end wall.
 4. The combustor assembly of claim3, wherein the ignition source resides on the side wall of the auxiliarycombustion chamber and at least a portion of the ignition sourceprotrudes radially into the space of the recirculation zone.
 5. Thecombustor assembly of claim 1, wherein the auxiliary combustion chamberis substantially cylindrical in shape, with the side wall having acircular cross-section of constant diameter, and the first and secondend walls being substantially planar.
 6. The combustor assembly of claim1, wherein the igniter body further comprises a fluid swirler residingat an entrance to the premixing cup residing within the auxiliarycombustion chamber.
 7. The combustor assembly of claim 6, wherein thefluid swirler comprises an axial fluid swirler comprising acircumferential pattern of swirl opening surrounding an outlet of theauxiliary fuel injector.
 8. The combustor assembly of claim 1, whereinthe torch igniter further comprises a shielding device configured to atleast partially shield the ignition source from fluid flow through theauxiliary combustion chamber.
 9. The combustor assembly of claim 8,wherein the shielding device is coupled to the inner surface of theauxiliary combustion chamber proximate the ignition source, andcomprises a curved, convex surface.
 10. The combustor assembly of claim9, wherein the convex surface of the shielding device faces the firstend wall of the auxiliary combustion chamber.
 11. The combustor assemblyof claim 10, wherein the convex surface of the shielding devicecomprises a plurality of apertures configured to permit a limitedportion of a fuel/air mixture to flow passed a tip of the ignitionsource.
 12. The combustor assembly of claim 1, wherein the torch igniterfurther comprises: an auxiliary fuel source in fluid communication witha nozzle orifice of the auxiliary fuel injector, the auxiliary fuelsource configured to provide a pressurized flow of fuel for injectioninto the auxiliary combustion chamber by the auxiliary fuel injector;and a bypass line configured to return at least a portion of thepressurized flow of fuel to a main engine fuel manifold.
 13. Thecombustor assembly of claim 1, wherein the outer shell comprises ahousing supporting the auxiliary fuel injector and the ignition source,and wherein the ignition source is mounted directly to the housing. 14.The combustor assembly of claim 13, wherein the fluid inlet of the outershell is defined by a bulkhead mounted directly to the housing.
 15. Thecombustor assembly of claim 1, wherein a density of the distributedpattern of cooling apertures varies along a longitudinal direction ofthe side wall of the auxiliary combustion chamber.
 16. The combustorassembly of claim 15, wherein the density increases in a downstreamlongitudinal direction toward the second end wall.
 17. A method ofoperating a gas turbine combustor assembly, the method comprising:mixing auxiliary fuel and air flows in an auxiliary combustion chamberto form an auxiliary fuel/air mixture wherein a premixing cup resides inthe auxiliary combustion chamber; igniting the auxiliary fuel/airmixture to form an auxiliary flow of heated fluid; directing theauxiliary flow of heated fluid downstream through the auxiliarycombustion chamber towards a primary combustion chamber; while directingthe auxiliary flow of heated fluid downstream, receiving, in an annulusdefined by an inner surface of an outer shell and an outer surface ofthe auxiliary combustion chamber, an upstream fluid flow, and directingthe upstream fluid flow so as to: form, with a first portion of theupstream fluid flow, a dilution flow directed into the downstreamauxiliary flow of heated fluid to dilute the heated fluid; form, with asecond portion of the upstream fluid flow, a film of cooling fluid alongan inner surface of the auxiliary combustion chamber; and form, with athird portion of the upstream fluid flow, the auxiliary air flow; andigniting a primary air/fuel mixture in the primary combustion chamber ofthe gas turbine combustor assembly with the auxiliary flow of heatedfluid from the auxiliary combustion chamber.